1. Field of the Invention
The general field of the invention is that of systems for managing aeronautical missions comprising a cartographic display. The more particular field of the invention is that of managing the display and the cartographic representation of various data in the case of a change of scale.
2. Description of the Prior Art
These systems are used on the ground for carrying out mission preparations or on board aircraft on systems installed on board and operating in real time. They therefore allow the preparation, monitoring or modification of the mission.
The purpose of these systems is to provide an overall, clear and consistent view of the situation of the aircraft in its environment. The principal items of information to be displayed are the navigation data:                Airports and heliports;        Navigation beacons of the following types: NDB (Non Directional Beacon), VOR (VHF Omnidirectional Range), DME (Distance Measuring Equipment), VORDME, TACAN (TACtical Air Navigation), VORTAC, ILS (Instrument Landing System);        Aeronautical waypoints or “Waypoints”;        Procedures of the air route, or “airways” type: SID (Standard Instrument Departure), STAR (Standard Terminal Arrival Route), APP (Approaches);        Air sectors or “airspaces”.        
All of the above data are present in databases in standardized formats like the ARINC 424 or “Navigation System Data Base Standard” type. The data relating to point, linear or surface obstacles are also critical for aeronautical systems. These data relating to obstacles are also present in databases.
A system for managing aeronautical missions essentially comprises four main sections shown in FIG. 1 and which are:                A tool for preparing the database denoted “tools”;        The database itself or “Database” or “DB”;        A computer or “Processing” whose functions are to select the useful data intended to be displayed as a function of the terrain flown over, of the selected scale and a certain number of factors depending on the flight or on the mission;        Finally, one or more display devices displaying the selected data and denoted “Display” in FIG. 1.        
The installation of such a system must meet two main objectives. The ergonomics of the interface must ensure the best possible legibility of the selected data and their consistency and display continuity when the scale changes. The system must operate in real time with a limited memory space. It is therefore necessary to optimize the amount of disk space necessary and the workload of the computer. Keeping to these objectives gives rise to a certain number of problems as described in detail below.
There is a very large amount of data to be displayed. At large scales, those corresponding to a country or a region, it cannot be envisaged to display all of the data because too much information is no longer legible.
In order to favour good comprehension of a complex display, it is necessary to provide good continuity of display when the user changes scale or representation. This change can take place continuously or in steps. In all cases, the system must display a legible and consistent display at each intermediate step. The continuity of display must also make it possible to avoid “flashing” effects, that is to say an element or an item of data that disappears at a certain scale and must no longer reappear at a larger scale.
In order to solve these different problems the existing solutions are of two types. It is possible to carry out a filtering of information either at the level of the DB or at the processing level.
Filtering information at the level of the DB is standard at the present time. This solution is applicable in all industrial and consumer presentations. It consists in constructing several databases with different levels of precision of the various items of information. Each DB is constructed to allow optimum rendering at a given scale. Dynamically, the cartographic system uses the optimum database closest to the current scale.
This solution has the following disadvantages:                Absence of display continuity for continuous scale changes. The change from one database to another results in a sudden change in representation which is not compatible with the need for continuity in the display. The change from one database to another generally necessitates a time period or latency. The associated transient processing which corresponds to a complete erasure of the image or to an incomplete image or to a blocking of interaction with the system reinforces the sensation of discontinuity in the display;        Large memory volume necessary. The solution necessitates the construction of several databases, and therefore of duplicating them. The necessary memory volume consequently increases. This is not detrimental to solutions accessing a DB via a “Web” interface. On the other hand, this problem is very detrimental to for a stand-alone on-board database present in an avionic system.        
When filtering information at the processing level, the system dynamically calculates the optimum quantity of elements to be displayed at a given scale as a function of filtering rules making it possible to select said elements. The term “decluttering” is also used. The following can be mentioned as examples of dynamic filtering rules:                Do not exceed a maximum number of elements displayed per type of object;        No longer display certain objects above a certain scale;        Establish a hierarchy of priorities of objects as a function of their type;        Establish a hierarchy of priorities of objects as a function of their distance from the aircraft.        
This latter solution has three disadvantages as described in detail below:                Complexity of the “decluttering” rules. The “advanced” decluttering rules such as, for example, the detection of graphical overlapping of close objects, necessitate complex calculations carried out dynamically. The dynamic implementation of advanced rules has poor performance on top of the range consumer equipment and is totally incompatible with present day avionic computers.        Complex updating procedures. In order to evolve a representation bound to a rule, it is systematically obligatory to modify the software.        Display continuity could be improved. In order to solve the problems mentioned above, the existing systems implement a compromise which is generally carried out to the detriment of the display continuity.        
It should be noted that certain solutions used for consumer applications combine both methods in order to try to reduce the problems encountered, without however totally solving them.